This invention relates generally to radiant ovens and more particularly to radiant ovens having increased cooking speed and efficiency while minimizing photochemical reactions in the cooked food.
Radiant ovens have been used to achieve higher cooking speed as compared to conventional ovens while maintaining a high food quality in an energy efficient manner. Such radiant ovens typically include a cooking chamber having highly reflective inner walls and a rack or the like within the cooking chamber upon which food items can be placed. Radiant ovens also include a means for producing radiant energy in the cooking chamber. Typically, the radiant energy means is an array of high-power lamps such as quartz-halogen lamps or quartz arc lamps. The lamps, which are ordinarily placed above and below the rack, radiate energy in all directions. A portion of the energy will radiate directly onto the food item, and the remainder of the energy will be reflected off of the inner walls of the chamber and then strike the food item for more efficient cooking. Sometimes, curved reflectors are placed behind the lamps so as to concentrate reflected energy onto the food item.
Typical quartz-halogen lamps convert electrical energy into radiation that follows a black body spectral distribution with a peak intensity at about 1 .mu.m wavelength. It is believed that the cooking action in most foods is primarily by absorption of so-called near infrared radiation, which is radiation having a wavelength in the range of about 1 .mu.m to 2.5 .mu.m. Radiation having somewhat longer wavelengths (sometimes referred to as the far infrared region) does not penetrate deeply into foodstuffs, but can be useful for the surface browning of foods. It is generally believed that radiation with wavelengths shorter than 1 .mu.m is not of much value in cooking processes, partly because of the weaker interaction of the shorter wavelengths with the food molecules, and partly because of the inferior food penetrating capability of such radiation. In particular, it is believed that visible light, i.e., radiation with a wavelength in the range of about 300 nm to 700 nm, is not very useful in cooking processes. In a typical radiant oven, the fraction of radiant energy in the visible light range that impinges on the foodstuff is approximately 10 to 15% of the total energy emitted to 2.5 .mu.m. Thus, although conventional radiant ovens are generally energy efficient as compared to most other cooking modalities, efficiency does suffer because a significant portion of the radiant energy impinging on the food contributes little to the cooking of the food.
Moreover, a portion of the visible spectrum is believed to be responsible in initiating undesired photochemical reactions in foodstuff through a nonlinear absorption process for foodstuff having UV absorption bands in the 250 nm to 290 nm range, a range which is common to all proteins. Because of the high intensity of the lamps, it is possible for food molecules to achieve an electrically excited state in which the molecules can emit heat, fluoresce, or undergo intersystem crossing and the breaking of a bond. Although the probability of bond rupture is relatively low, the consequences are that free radicals (unpaired electrons on the molecular product fragments) are produced each time a molecule undergoes such excited state deactivation. Since free radicals are very reactive with other molecules, this can lead to the possibility of considerable chemical changes in foodstuffs cooked in a conventional radiant oven, including the loss of food nutrients and the formation of undesired products. The critical spectral component of this free radical formation process falls in the visible spectrum.
Speed of cooking is another factor that differentiates radiant ovens from conventional cooking, and even greater cooking speeds would be advantageous. Yet, cooking speed does not necessarily increase with increased energy flux. This is because, as mentioned above, a large portion of the lamp power does not penetrate far into the surface of the food. If the influx of radiant energy is very much higher than the rate of thermal diffusion in from the surface, the food will char and burn at the surface. The charring starts a cycle that further prevents energy penetration into the interior. The result is a food that is badly burned at the surface and unacceptable in quality. Thus, simply increasing energy flux is not an effective approach to increasing cooking speed. A further practical limitation arises in that the amount of available radiant energy in a standard oven design is limited by the maximum capacity of an ordinary household electrical power circuit, which is 18 kW.
Finally, because of the high rate of surface heating in conventional radiant ovens, the cook times and power levels of the lamps are very sensitive to food type, size and placement in the oven.
Accordingly, there is a need for a radiant oven that cooks food faster without burning, is more efficient, has more robust cooking control, and avoids undesired photochemical reactions.